Multiple facet joint replacement

ABSTRACT

A prosthesis for the replacement of multiple diseased or traumatized spinal facets comprises a portion that replaces at least a bony portion of the facets to be replaced and where the prosthesis attaches to the vertebra in a manner that does not require attachment to, or abutment against, the lamina. Multiple configurations of the prosthesis provide for replacement of the two inferior facets, the two superior facets, a superior and inferior facet, or all four facets. A method of installing the prosthesis is provided that is comprised of the steps of resecting at least a portion of the facets that carry the diseased or traumatized spinal facets and attaching the prosthesis in a manner that does not require attachment or abutment against the lamina.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of:

U.S. application Ser. No. 10/420,467, filed Apr. 22, 2003 now U.S. Pat.No. 7,074,237, and entitled MULTIPLE FACET JOINT REPLACEMENT,

Which is a continuation of:

U.S. application Ser. No. 09/736,103, filed Dec. 13, 2000 now U.S. Pat.No. 6,565,605 and entitled MULTIPLE FACET JOINT REPLACEMENT.

The disclosures listed above are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. The Field of the Invention

The present invention relates to surgical devices and methods to replacea damaged, diseased, or otherwise painful spinal facet joint.

2. Description of Related Art

Traumatic, inflammatory, metabolic, synovial, neoplastic anddegenerative disorders of the spine can produce debilitating pain thatcan have severe socioeconomic and psychological effects. One of the mostcommon surgical interventions today is arthrodesis, or spine fusion, ofone or more motion segments, with approximately 300,000 proceduresperformed annually in the United States. Clinical success variesconsiderably, depending upon technique and indications, andconsideration must be given to the concomitant risks and complications.For example, it has been shown that spine fusion decreases function bylimiting the range of motion for patients in flexion, extension,rotation, and lateral bending. Furthermore, it has been shown that spinefusion creates increased stresses and, therefore, accelerateddegeneration of adjacent non-fused motion segments. Additionally,pseudoarthrosis, as a result of an incomplete or ineffective fusion, mayreduce or even eliminate pain relief for the patient. Also, the fusiondevice, whether artificial or biological, may migrate out of the fusionsite.

Recently, several attempts have been made to recreate the naturalbiomechanics of the spine by use of an artificial disc. Artificial discsprovide for articulation between vertebral bodies to recreate the fullrange of motion allowed by the elastic properties of the naturalintervertebral disc which directly connects two opposed vertebralbodies.

However, the artificial discs proposed to date do not fully address themechanics of motion of the spinal column. In addition to theintervertebral disc, posterior elements called the facet joints help tosupport axial, torsional and shear loads that act on the spinal column.Furthermore, the facet joints are diarthroidal joints that provide bothsliding articulation and load transmission features. The effects oftheir absence as a result of facetectomy has been observed to producesignificant decreases in the stiffness of the spinal column in allplanes of motion: flexion and extension, lateral bending, and rotation.Furthermore, contraindications for artificial discs include arthriticfacet joints, absent facet joints, severe facet joint tropism orotherwise deformed facet joints.

U.S. Pat. No. Re. 36,758 to Fitz discloses an artificial facet jointwhere the inferior facet, the mating superior facet, or both, arecovered with a cap. The cap requires no preparation of the bone orarticular surfaces; it covers and, therefore, preserves the bony andarticular structure.

The capping of the facet has several potential disadvantages. If thefacet joint is osteoarthritic, a cap will not remove the source of thepain. Additionally, at least in the case of surface replacements forosteoarthritis femoral heads, the capping of articular bone ends hasproven to lead to clinical failure by means of mechanical loosening. Theclinical failure is hypothesized to be a sequela of disrupting theperiosteum and ligamentum teres femoris, both serving a nutritiondelivery role to the. femoral head, thereby leading to avascularnecrosis of the bony support structure for the surface replacement.Another potential disadvantage is that in order to accommodate the widevariability in anatomical morphology of the facets, not only betweenindividuals but also between levels within the spinal column, a verywide variety of sizes and shapes would be required.

U.S. Pat. No. 6,132,464 to Martin discloses a spinal facet jointprosthesis that is supported on the lamina, which is sometimes alsoreferred to as the posterior arch of the vertebra. Extending from thisprosthetic support structure are inferior and/or superior blades thatreplace the cartilage at the facet joint. Like the Fitz design, theMartin prosthesis generally preserves existing bony structures andtherefore does not address pathologies which affect the bone of thefacets in addition to affecting the associated cartilage. Furthermore,the Martin invention requires a mating condition between the prosthesisand the lamina, or the posterior arch, that is a thin base of curvedbone that carries all four facets and the spinous process. Since theposterior arch is a very complex and highly variable anatomic surface,it is very difficult to design a prosthesis that provides reproduciblepositioning to correctly locate the cartilage-replacing blades for thefacet joints.

Another approach to surgical intervention for spinal facets is providedin WO9848717A1 to Villaret. While Villaret teaches the replacement ofspinal facets, the replacement is interlocked in a manner to immobilizethe joint.

Facet joint replacement in conjunction with artificial disc replacementsrepresent a novel solution to recreating a fully functional motionsegment that is compromised due to disease or trauma. Together, facetjoint and disc replacement can eliminate substantially all sources ofpain, return full function and range of motion, and restore the naturalbiomechanics of the spinal column. Additionally, degenerative ortraumatized facet joints may be replaced in the absence of discreplacement when the natural intervertebral disc is unaffected by thedisease or trauma.

It would therefore be an improvement in the art to provide a device anda method for the replacement of multiple vertebral facets and a portionof their associated bony structure so as to remove the source oftraumatic, arthritic, or other disease related pain.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a multiple vertebral facetreplacement prosthesis for a diseased or traumatized vertebra withpainful or compromised facet joints.

It is another object of the invention to provide a method of replacingmultiple vertebral facets for a diseased or traumatized vertebra withpainful or compromised facet joints.

It is yet another object of the present invention to provide a kit ofmultiple facet prostheses for the convenient replacement of one or morelevels of facet joints.

In one preferred embodiment, the inferior bilateral facets of a superiorvertebra are resected at the base of the facets where they connect tothe posterior arch. Flanges are oriented relative to the body of theprosthesis such that when the flanges are placed against the pediclesand in a manner such that the planar surfaces of the flanges areperpendicular to the respective axes of the pedicle's interior bonecanal, the articulating surfaces of the inferior bilateral facetprosthesis will be properly positioned to replicate the articulatingsurfaces of the natural facets. Each flange includes a hole for thepassage of a fastener to securely attach the prosthesis to the pedicle.The fastener can be a screw, spike, tack, staple, modular post, or thelike.

Alternatively, or in addition, the superior facets of an inferiorvertebra are resected at the base of the facets where they connect tothe pedicles. As with the bilateral inferior facet prosthesis, abilateral superior facet prosthesis is attached to the inferior vertebraby means-of fasteners which engage holes on mounting flanges and thepedicles.

The fasteners or the bone contacting surfaces of the flanges may beporous coated to promote bone ingrowth in order to achieve long termfixation. The porous coating may carry osteoconductive agents, such ashydroxylapatite, calcium sulfate, or demineralized bone matrix.Alternatively, the porous coating may carry osteoinductive agents, suchas bone morphogenic proteins, including rhBMP-2 and rhBMP-7.

Alternative embodiments of the present invention include the replacementof different combinations of facets on a single vertebra. One embodimentprovides for the replacement of the left inferior and left superiorfacets by a single prosthesis. Another embodiment provides for theconcurrent replacement of all four facets by a single prosthesis. Thefour facet prosthesis can be used in conjunction with a superiorbilateral facet replacement and an inferior bilateral facet replacementto provide a two level replacement of facet joints. Alternatively, twoof the four facet prostheses can be used in conjunction with a superiorbilateral facet replacement and an inferior bilateral facet replacementto provide a three level replacement of facet joints, where the middlelevel facet replacement is accomplished by the two adjacent four facetprostheses.

The present invention has numerous advantages over the prior art. Amongother things, the present invention provides for the convenient,simultaneous replacement of multiple combinations of facets on a singlevertebra: two superior facets, two posterior facets, two left facets,two right facets, or all four facets. Furthermore, multiple levels offacet joints can be replaced by selecting from a kit of multiple facetjoint prostheses. Another advantage of the present invention is aprecise and tight attachment of the prosthesis to bones, as opposed toprosthetic surfaces that rely on mating with highly complex and variableexternal surfaces of the vertebra, such as the posterior arch. Anotheradvantage is that the optional porous coating is placed into interiorbone spaces where porous coatings have proven to achieve bone ingrowthfor excellent long term fixation strength. This ability to achieve boneingrowth is uncertain for the prior art devices that engage the externalbone surfaces of the vertebra. Yet another advantage lies in the removalof the facet bone structure. More particularly, where the facet bone isinvolved in the disease pathology or the trauma that compromised thearticular or cartilaginous surface of the facet, resection provides ameans for ensuring that all pain associated with the disease or traumais removed. With prior art devices, the bony structure of the facets isgenerally left intact.

The above, and other, objects, features and advantages of the presentinvention will become apparent from the following description which isto be read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a spine motion segment;

FIG. 2 is a dorsal view of a bilateral facet joint reconstructed inaccordance with the present invention;

FIG. 3 is a lateral view of the bilateral facet joint prosthesis shownin FIG. 2;

FIG. 4 is a dorsal view of the implanted inferior bilateral facetprosthesis shown in FIGS. 2 and 3;

FIG. 5 is an inferior view of the implanted inferior bilateral facetprosthesis shown in FIGS. 2 and 3;

FIG. 6 is a ventral view of the inferior bilateral facet prosthesisshown in FIGS. 4 and 5;

FIG. 7 is a dorsal view of the implanted superior bilateral facetprosthesis shown in FIGS. 2 and 3;

FIG. 8 is a superior view of the implanted superior bilateral facetprosthesis shown in FIGS. 2 and 3;

FIG. 9 is a ventral view of the superior bilateral facet prosthesisshown in FIGS. 7 and 8;

FIG. 10 is a perspective view of an alternative embodiment of thesuperior bilateral facet prosthesis shown in FIGS. 7 and 8;

FIG. 11 is a dorsal view of a two level facet joint replacement;

FIG. 12 is a lateral view of the two level facet joint replacement ofFIG. 11;

FIG. 13 is a dorsal view of the implanted four facet prosthesis shown inFIGS. 11 and 12;

FIG. 14 is a perspective view of the four facet prosthesis shown in FIG.13;

FIG. 15 is a perspective view of an alternative form of inferiorbilateral facet prosthesis;

FIG. 16 is a perspective view of an implanted superior and inferiorunilateral facet prosthesis; and

FIG. 17 is a perspective view of the unilateral facet prosthesis shownin FIG. 16.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring first to FIG. 1, there is shown a superior vertebra 5 and aninferior vertebra 10, with an intervertebral disc 15 located in between.Vertebra 5 has superior facets 20, inferior facets 25, a lamina (alsosometimes referred to as a posterior arch) 30, a spinous process 35, andpedicles 40. Vertebra 10 has superior facets 45, inferior facets 50, aposterior arch 55, a spinous process 60, and pedicles 65 (only one ofwhich is seen in FIG. 1).

Referring now to FIG. 2, the left and right inferior facets 25 ofvertebra 5 have been resected at 70 and a bilateral inferior facetprosthesis 75 has been attached to vertebra 5 using screw fasteners 80.Similarly, the left and right superior facets 45 of vertebra 10 havebeen resected at 82 (FIG. 7) and a bilateral superior facet prosthesis85 has been attached to vertebra 10 using screw fasteners 90.

In FIG. 3 it can be appreciated that bilateral inferior facet prosthesis75 replicates the natural anatomy when compared to the intact inferiorfacet 25 of vertebra 5. Furthermore, bilateral facet prosthesis 75extends from its attachment point in a manner that does not requirecontact with, or mating to, the complex geometry of the lamina (orposterior arch) 30. Resection surfaces 70 provide adequate clearance forbilateral inferior facet prosthesis 75 and provide complete removal ofthe diseased or traumatized natural inferior facets 25.

FIGS. 4 and 5 illustrate how the geometry of the bridge 95 of bilateralinferior facet prosthesis 75 matches that of the posterior arch 30 ofvertebra 5 in order to provide adequate clearance for the centralforamen 100. Articular surfaces 105 articulate with the opposingsuperior facets 45 (or their prosthetic replacements) of the vertebra10.

FIG. 6 illustrates the bilateral inferior facet prosthesis 75 withflanges 110 that abut against the pedicles 40 of vertebra 5. Bridge 95connects the articular surfaces 105. Holes 115 allow the attachment ofbilateral inferior facet prosthesis 75 to vertebra 5 by means of screwfasteners 80. Alternatively, screw fasteners 80 could be replaced withstaples, pins, tacks, anchors, modular fixation posts, or the like.These alternative fasteners could further include porous coatings tofurther enhance bony fixation, and could also include osteoconductive orosteoinductive substances.

In FIG. 7 it can be appreciated that bilateral superior facet prosthesis85 replicates the natural anatomy when compared to the intact superiorfacets 45 of vertebra 10. Furthermore, bilateral facet prosthesis 85extends from its attachment point in a manner that does not requirecontact with, or mating to, the complex geometry of the lamina (orposterior arch) 55. Resection surfaces 82 provide adequate clearance forbilateral superior facet prosthesis 85 and provide complete removal ofthe diseased or traumatized natural superior facets 45.

FIG. 8 illustrates how the geometry of the bridge 120 of bilateralsuperior facet prosthesis 85 matches that of the posterior arch 55 ofvertebra 10 in order to provide adequate clearance for the centralforamen 125. Articular surfaces 130 articulate with the opposinginferior facets of the vertebra 5.

FIG. 9 illustrates the bilateral superior facet prosthesis 85 withflanges 135 that abut against the pedicles 65 of vertebra 10. Bridge 120connects the articular surfaces 130 (seen in FIG. 8 but not seen in FIG.9). Holes 140 allow the attachment of bilateral superior facetprosthesis 85 to vertebra 10 by means of screw fasteners 90.

FIG. 10 illustrates an alternative superior facet prosthesis 85A with abearing surface 130A that mounts to substrate 131A. The bearing surface130A is preferably a biocompatible polymeric material, such as ultrahigh molecular weight polyethylene. Alternately, the bearing surface130A can be ceramic, such as zirconia or alumina. The substrate 131A ispreferably a biocompatible metal alloy, such as an alloy of titanium,cobalt, or iron.

FIG. 11 illustrates a superior vertebra 145, a middle vertebra 150, andan inferior vertebra 155. Superior facet prosthesis 85 articulates withquad-facet prosthesis 160 to recreate the natural biomechanics of thereplaced facet joints. Inferior facet prosthesis 75 articulates withquad-facet prosthesis 160 to recreate the natural biomechanics of thereplaced facet joints at the next upper level. Thus, FIG. 11 illustratesa two level reconstruction of facet joints. Superior facet prosthesis85, quad-facet prosthesis 160, and inferior facet prosthesis 75 are eachattached to bone by means of screw fasteners 165.

In the lateral view of FIG. 12, it can be appreciated that superiorfacet prosthesis 85, quad-facet prosthesis 160, and inferior facetprosthesis 75 do not encroach into the intervertebral foraminal spaces167 where nerve roots extend laterally from the spinal cord.

Referring next to FIG. 13, it should be appreciated that superior bridge170 and inferior bridge 175 of quad-facet prosthesis 160 do not contactany portion of vertebra 150. Mounting holes 180 (shown in FIG. 14) areused to secure the flanges 185 against the pedicles of vertebra 150.

In FIG. 15, an alternative inferior bilateral facet prosthesis 190 ispresented. To further stabilize the implant and to counter moments thatact upon the two points of fixation into the pedicles, a set of parallelflanges 195 extend posteriorly such that the two flanges straddle thespinous process 35. A bolt 200 is used to fasten the parallel flanges tothe spinous process. Alternatively, other adjunctive structural featurescould be added to further stabilize the prosthesis. For example, a strutthat extends, and attaches, to the transverse process could be used tofurther stabilize the prosthesis. It can be appreciated that the bridge95 of alternative bilateral facet prosthesis 190 extends between theleft and right articular surfaces 105 (as best seen in FIG. 6) andoccupies a volume 205 between the articular surfaces, as shown in dashedlines in FIG. 15. The volume 205 may be defined by projecting theoutline of an articular surface 105 along a straight path between twoarticular suffaces. It can be appreciated that articular surfaces 105 ofdifferent shapes or sizes would have different outlines, thus definingvolumes 205 of different shapes or sizes.

Looking next at FIGS. 16 and 17, there is shown a superior and inferiorunilaterial facet prothesis 300. Unilaterial facet prothesis 300comprises a body 305 and a stem 310 extending out of body 305. Asuperior element 315 extends vertically upward from body 305, and aninferior element 310 extends vertically downward from body 305.Unilateral facet prosthesis 300 is configured so that when its stem 310extends into the pedicle of vertebra 325, superior element 315 willreplace a resected superior facet, and inferior element 320 will replacea resected inferior facet. If desired, stem 310 could be replaced with ascrew extending through a hole in body 305 and into the pedicle.

Having described preferred embodiments of the invention with referenceto the accompanying drawings, it is to be understood that theembodiments shown herein are by way of example and not limitation, andthat various changes and modifications may be effected by one skilled inthe art without departing from the scope or spirit of the invention asdefined in the following claims.

1. An implant for replacing at least a left inferior facet and a right inferior facet of a first vertebra comprising a natural lamina, a natural left inferior facet, and a natural right inferior facet, the implant comprising: a left inferior articular surface shaped to replace the natural left inferior facet; a right inferior articular surface shaped to replace the natural right inferior facet; and a bridge extending along a substantially straight path between the left and right articular surfaces to couple the left and right inferior articular surfaces together; wherein the bridge comprises a cross sectional shape perpendicular to the path that remains uniform over at least a portion of a length of the path.
 2. The implant of claim 1, wherein the left and right inferior articular surfaces are attachable to the first vertebra independently of attachment to a transverse process of the first vertebra.
 3. The implant of claim 1, wherein the cross sectional shape remains substantially uniform along substantially all of the length of the path.
 4. The implant of claim 1, wherein the path extends substantially medial-laterally.
 5. The implant of claim 1, wherein the left and right inferior articular surfaces are positioned substantially in-line with the path.
 6. The implant of claim 1, wherein the bridge couples the left and right inferior articular surfaces together in such a manner that the left and right inferior articular surfaces are non-adjustably positionable relative to each other.
 7. The implant of claim 6, wherein the left and right inferior articular surfaces are formed as a single piece with the bridge.
 8. An implant for replacing at least a left facet and a right facet of a first vertebra comprising a natural lamina, a natural left facet, and a natural right facet, the implant comprising: a left articular surface shaped to replace the natural left facet; a right articular surface shaped to replace the natural right facet; and a bridge extending along a substantially straight path to couple the left and right articular surfaces together such that the left and right articular surfaces are positioned substantially in-line with the substantially straight path; wherein the bridge comprises a cross sectional shape perpendicular to the path that remains uniform over at least a portion of a length of the path.
 9. The implant of claim 8, wherein the left and right articular surfaces are attachable to the first vertebra independently of attachment to a transverse process of the first vertebra.
 10. The implant of claim 8, wherein the cross sectional shape remains substantially uniform along substantially all of the length of the path.
 11. The implant of claim 8, wherein the path extends substantially medial-laterally.
 12. The implant of claim 8, wherein the left and right articular surfaces comprise left and right inferior articular surfaces shaped to articulate with left and right superior articular surfaces of a second vertebra inferior to the first vertebra.
 13. The implant of claim 8, wherein the bridge couples the left and right articular surfaces together in such a manner that the left and right articular surfaces are non-adjustably positionable relative to each other.
 14. The implant of claim 13, wherein the left and right articular surfaces are formed as a single piece with the bridge.
 15. An implant for replacing at least a left facet and a right facet of a first vertebra comprising a natural lamina, a natural left facet, and a natural right facet, the implant comprising: a left articular surface shaped to replace the natural left facet; a right articular surface shaped to replace the natural right facet; and a bridge formed as a single piece with the left articular surface and the right articular surface to couple the left and right articular surfaces together; wherein the bridge occupies a volume between the left and right articular surfaces; wherein at least one of the left and right articular surfaces comprises an inferior articular surface shaped to articulate with a superior articular surface of a second vertebra inferior to the first vertebra.
 16. The implant of claim 15, wherein the left and right articular surfaces are attachable to the first vertebra independently of attachment to a transverse process of the first vertebra.
 17. The implant of claim 15, wherein the bridge comprises a cross sectional shape that remains substantially uniform along substantially all of the length of the path.
 18. The implant of claim 15, wherein the bridge extends along a substantially straight path between the left and right articular surfaces.
 19. The implant of claim 15, wherein the path extends substantially medial-laterally.
 20. The implant of claim 15, wherein the left and right articular surfaces comprise left and right inferior articular surfaces shaped to articulate with left and right superior articular surfaces of a second vertebra inferior to the first vertebra. 